The state of clay dispersion in maleated polypropylene/organoclay nanocomposites via dielectric spectroscopy measurements

Abstract

Dielectric spectroscopy is a powerful method that allows the study of dynamics of polymers in a wide frequency range. In this work, the state of clay dispersion was related to the dielectric properties of the polymer nanocomposites based on organoclay filled maleated polypropylene (PPgMA). Fully and partially exfoliated samples were prepared through powered sonication and melt blending, respectively. Though two mechanical relaxations were revealed from dynamical mechanical analysis (DMA), only a single high-temperature process resulting from interfacial polarization was observed in broadband dielectric measurements. Dielectric dispersion parameters that appear sensitive to clay loading and degree of exfoliation were identified. The nanomorphology was primarily reflected in the Maxwell-Wagner characteristic relaxation frequency value, fp, where samples with higher degree of exfoliation showed lower relaxation rate. The relaxation time constant, which is the reciprocal of 2πfp, can be correlated with mean distance of clay layer separation in the nanocomposites and therefore provides additional information on exfoliation of clay platelets. A clear evolution of the relaxation activation energy with the degree of clay dispersion was also observed. The experimental results indicated that sonicated samples with fully exfoliated clay platelets yielded the longer relaxation time and the higher activation energy compared to their partially exfoliated counterparts.